Railways Technical Ability Metal Forming, Casting and Cutting Question Bank Metal Casting

  • question_answer A spherical drop of molten metal of radius 2 mm was found to solidify in 10 seconds. A similar drop of radius 4 mm would solidify in:

    A) 14.14 second                 

    B) 20 seconds

    C) 18.30 second                 

    D) 40 seconds

    Correct Answer: D

    Solution :

    Solidification time for a sphere, \[t\,\alpha {{\left( \frac{V}{A} \right)}^{2}}\] \[\frac{V}{A}=\frac{\left( \frac{4}{3}\pi {{r}^{3}} \right)}{4\pi {{r}^{2}}}=\frac{r}{3}\] \[t\propto {{r}^{2}}\] \[\frac{{{t}_{2}}}{{{t}_{1}}}={{\left( \frac{4}{3} \right)}^{2}}=4\] \[{{t}_{2}}=4\times 10=40s\]

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